1. Field of the Invention
The present invention generally relates to a powder feeding device that feeds powder such as toner to a developing device used in an image forming apparatus such as a copier, a facsimile machine, a printer and the like, and an image forming apparatus including the powder feeding device.
2. Description of the Related Art
There have been known various powder feeding devices feeding toner (powder) from a toner container as a powder container to a developing device. The powder feeding devices have been used in various image forming apparatuses including a copier, a facsimile machine, a printer and the like. Further, there have been proposed various powder feeding devices in which heat stress on toner is reduced to prevent the aggregation of toner powder and prevent fixing the toner to the inner surface of a feeding path when the toner includes thermoreversible resin or the like.
For example, Japanese Patent Application Publication No. 2009-175703 (hereinafter referred to as “Patent Document 1”) discloses a powder feeding device that feeds toner (powder) under a condition that heat stress on the toner is low as illustrated in FIG. 16. In the following description, since some terms and reference numerals used in Patent Document 1 are same or equivalent to those used in examples of the present invention described below, only different terms and reference numerals used in Patent Document 1 are described in parentheses.
As illustrated in FIG. 16, a powder feeding device 35 (developer feeding device 35A) of an image forming apparatus disclosed in Patent Document 1 includes a toner container 40 as a powder container containing toner (powder) 36. Further, the powder feeding device 35 includes a feeding tank 41 including an input port 49, an output port 50, and a suction port 51. The input port 49 is formed so that toner 36 supplied from the toner container 40 is input into the feeding tank 41 through the input port 49. The output port 50 is provided, so that the toner 36 is discharged from the feeding tank 41 to a container tank 17 of a developing device 13. The suction port 51 is provided, so that gas in the feeding tank 41 is discharged (suctioned) through the suction port 51. In the feeding tank 41, a feeding screw 42 is provided so that toner 36 supplied from the toner container 40 is fed to the output port 50 when the feeding screw 42 rotates. Further, a filter 55 is provided at the suction port 51. Further, a suction port communicating tube 45 (communication plumbing 45a) is provided to be connected to the suction port 51. Further, a negative pressure room (negative pressure tank) 82 is provided to be in communication with the feeding tank 41 via the suction-port communicating tube 45. Further, a suction-port opening and closing device (negative pressure room opening and closing device) 93 is provided as a suction-port opening and closing unit to open and close the inside of the suction-port communicating tube 45. Further, a negative pressure room communicating tube 100 (communication plumbing 45b) is provided to be connected to a through hole 88 which is a negative pressure room suction port formed on the negative pressure room 82. Further, the negative pressure room 82 includes a first negative pressure room 83 which is the upper part of the negative pressure room 82 and a second negative pressure room 84 which is the lower part of the negative pressure room 82. The first negative pressure room 83 is communication with the second negative pressure room 84 via an auxiliary filter 92. Further, the suction-port communicating tube 45 is in communication with the second negative pressure room 84 which is the lower part of the negative pressure room 82. Further, the first negative pressure room 83 which is the upper part of the negative pressure room 82 is in communication with a suction pump 43 via the through hole 88 and the negative pressure room communicating tube 100 (communication plumbing 45b), the through hole 88 being a negative pressure room suction port formed on the first negative pressure room 83. The suction pump 43 is provided as an air suction device communicating with the negative pressure room 82. Further, a suction pump 43 as a gas suctioning device is provided to be in communication with the negative pressure room 82 via the negative pressure room communicating tube 100. Further, a discharge tube 46 is provided to be connected to the output port 50. Further, there are provided a negative pressure room opening and closing device (suction pump opening and closing device) 96 and an output port opening and closing device (opening and closing device) 47. The negative pressure room opening and closing device 96 opens and closes the inside of the negative pressure room communicating tube 100 as a negative pressure room opening and closing unit. The output port opening and closing device 47 opens and closes the inside of the discharge tube 46 as an output port opening and closing unit. The other end of the discharge tube 46 is connected to a supply hole 37 of the container tank 17 of the developing device 13. Further, a mixing screw 18 to mix and feed the developer (toner) is provided in the container tank 17. Further, a pressure sensor 90 to detect the pressure in the negative pressure room 82 is provided. Further, a controller 48 to control the devices is provided. The controller 48 repeatedly performs a series of operations described below upon receiving a signal instructing supply of toner 36 to the developing device 13.
In the powder feeding device 35, toner 36 is supplied from the toner container 40 to the container tank 17 of the developing device 13 while maintaining heat stress on toner to be low by operating each component in the powder feeding device 35 as follows. The controller 48 causes a piston driving device 60 to move a piston 59 of the suction pump 43 to the position closest to a bottom part 61 of a cylinder main body 58. Then, the controller 48 causes an open and close driving source 71 of the output port opening and closing device 47 to close the inside of the discharge tube 46, causes a suction-port opening and closing device 95 of the suction-port opening and closing device 93 to close the inside of the suction-port communicating tube 45, and causes an open and close driving source 98 of the negative pressure room opening and closing device 96 to open the inside of the negative pressure room communicating tube 100. Under this state, the controller 48 controls to move the piston 59 so that the piston 59 is separated from the bottom part 61 of a cylinder main body 58. As a result, gas in the negative pressure room 82 is suctioned by the suction pump 43 and the pressure in the negative pressure room 82 is lowered. As a result, a negative pressure is generated in the negative pressure room 82, and namely, a negative pressure is generated in a first negative pressure room 83 and a second negative pressure room 84. Then, when the pressure in the negative pressure room 82 detected by the pressure sensor 90 becomes a predetermined value, the controller 48 stops the suctioning operation of the suction pump 43 and causes the open and close driving source 98 of the negative pressure room opening and closing device 96 to close the inside of the negative pressure room communicating tube 100. Then, the controller 48 controls to rotate the feeding screw 42 in the feeding tank 41 around the axle of the feeding screw 42 and causes the open and close driving source 95 of the suction-port opening and closing device 93 to open the inside of the suction-port communicating tube 45. As a result, gas in the feeding tank 41 is suctioned into the negative pressure room 82 due to the negative pressure in the negative pressure room 82. By suctioning gas in the feeding tank 41 into the negative pressure room 82 and reducing the pressure in the feeding tank 41, toner 36 along with gas in the toner container 40 are suctioned into the feeding tank 41.
Further, when air in the feeding tank 41 is suctioned by the negative pressure in the negative pressure room 82, the toner 36 having been suctioned (introduced) into the feeding tank 41 is also suctioned toward the negative pressure room 82. However, the filter 55 prevents the toner 36 from being passing through the filter 55. As a result, the leakage of the toner 36 beyond the suction port 51 is prevented. Further, the toner 36 having passed through the filter 55 is prevented from passing through the auxiliary filter 92, so the toner 36 remains in the first negative pressure room 83 and does not enter into the suction pump 43.
Then, after a predetermined time period has passed, the controller 48 causes the open and close driving source 95 of the suction-port opening and closing device 93 to close the inside of the suction-port communicating tube 45. As a result, the feed of toner from the toner container 40 to the feeding tank 41 is stopped, and toner in the feeding tank 41 is fed toward the output port 50 by the rotation of the feeding screw 42. After that, the controller 48 causes the open and close driving source 71 of the output port opening and closing device 47 to open the inside of the discharge tube 46. As a result, toner 36 in the feeding tank 41 is discharged to an outside of the feeding tank 41 via the output port 50, so that toner 36 is supplied into the container tank 17 of the developing device 13. As described above, the controller 18 of the powder feeding device 35 performs a series of control operations of generating a negative pressure in the negative pressure room 82, suctioning toner 36 into the feeding tank 41, and discharging toner 36 through the output port 50.
As described above, in the powder feeding device 35 of related art illustrated in FIG. 16, gas in the feeding tank 41 is suctioned so as to suction toner 36 from the toner container 40 into the feeding tank 41. Namely, in order to suction toner 36 into the feeding tank 41, a negative pressure is generated in the feeding tank 41. Further, in order to generate the negative pressure in the feeding tank 41, the suction pump 43 is provided outside the feeding tank 41. Because of this structure, it is possible to prevent the heat transfer from the suction pump 43 to toner 36. Further, since the negative pressure is used to suction toner 36 into the feeding tank 41, it becomes possible to suction toner 36 into the feeding tank 41 without grinding toner 36. As a result, it becomes possible to minimize the heat stress on toner 36 and feeding toner 36. Further, it becomes possible to generate a negative pressure in the negative pressure room 82 by suctioning gas in the negative pressure room 82 using the suction pump 43 and suction gas in the feeding tank 41 by using the negative pressure in the negative pressure room 82. Because of this structure, when compared with a case where, for example, gas in the feeding tank 41 is directly suctioned by a mechanical gas suctioning device such as the suction pump, a suction time period may be reduced and a feeding time of toner as powder may also be reduced.
Further, when compared with a case where a mechanical air suction device such as the suction pump is used to directly suction the air in the feeding tank 41, it may become possible to increase a feeding amount of toner 36 per unit time. Therefore, it may become possible to apply to an image forming apparatus having faster printing speed and having a larger toner consumption amount per unit time as well.
Further, due to the filter 55 provided at the suction port 51 and the auxiliary filter 92 provided between the first negative pressure room 83 and the second negative pressure room 84, the toner 36 is prevented from entering into the suction pump 43. By doing this, it may become possible to eliminate the direct contact between the toner 36 and the suction pump 43. Therefore, it may become possible to apply grease or the like to the suction pump 43. As a result, it may become possible to prevent a failure and a trouble of the suction pump 43 caused by the adhesion of the toner 36 to the suction pump 43 and lower the driving torque of the suction pump 43 and enhance the service lifetime of the suction pump 43.